Sialic acids are found in a diverse group of glycoprotein oligosaccharides. At least seven sialyltransferases are thought to be required to account for the variety of oligosaccharide structures observed. Three sialyltransferases have been purified to homogeneity, and each has a strict acceptor specificity which limits its transfer of sialic acid from CMP-sialic acid to an oligosaccharide of defined structure. To date, purified sialyltransferases have been instrumental in understanding the molecular basis for the inactivation of a hepatic galactoside binding protein by neuraminidase, the adsorption of certain myxoviruses to erythrocyte receptors, and the role of sialic acid in the expression of the human M and N blood group antigens. In the proposed research, three additional sialyltransferases which form the sequences SAalpha2, 3Galbeta1, 3G1cNAc, Galbeta,3(SAalpha2,6)GlcNAc and SAalpha2, 8SA, found in glycoprotein oligosaccharides will be identified and purified to homogeneity. Their enzymatic properties and substrate specificities will be established to deduce their role in oligosaccharide biosynthesis, and to determine their suitability to serve as specific reagents to examine the biological roles of sialic acids.